Rapid tanning sole leather using polyoxysaccharide bisulfites



United States Patent 3,114,589 RAPID TANNING SGLE LEATHER USING POLYOXYSACCHAREE BISULFITES Carlo Bellucci-Sessa, Milan, Italy, assignor to Ledoga S.p.A., Milan, Italy No Drawing. Filed Feb. 19, 1962, Ser. No. 174,236 Claims priority, application Italy Nov. 22, 1960 4 Claims. (Cl. 894.33)

This invention is concerned with a rapid tannin-g rocess for sole leather using polyoxysaccharide bisulfites.

Present vegetable tanning processes for production of sole leather, even if termed tanning, are carried out in tanks and drums and require from 34 to 55 days. This length of time is necessary because the combination between vegetable tannin and the protein of the pelts is not a vigorous reaction, and it" it is not suitably controlled, leads to undesirable results and to a finished product of poor chemical and physical qualities and of limited commercial value,

This is a continuation-in-part of my copending application Serial No. 150,877, filed on November 8, 1961.

Before the tanning step, cattle hides destined for processing into sole leather are subjected to a series of preliminary treatments which must be previously removed, such as fur and flesh, so that tanning is carried out on pure dermic substance.

If a hide so prepared comes into contact with a highly concentrated vegetable tannin solution, fixing of the tanning agent takes place very rapidly, but is limited to the external surfaces of the hide, and the combination is all the more rapid the greater the astringency of the vegetable tanning agent used. This surface tanning has a negative influence on the tanning process as it hinders the regular diffusion of the tanning agent through the internal layers of the hide, besides producing shrivelling of the grain. This is also due to the large size of the colloidal micelles present in vegetable tanning solutions.

In conventional tanning processes, the control of the reaction between protein and vegetable tannin is effected by diving hides into tanning solutions of increasing concentration from 23 Be. to 1819 Be'., While the pH decreases from an initial value of 5.5 to a final value of 3.5. By this means, the hides follow a counter-current course so that they come into contact with dilute and aged baths during the first stages of tanning, While at the end, the baths are more concentrated and fresh. All the above accounts for the need to carry out tanning with a continuous and lengthy process, which is also expensive and bothersome with regard to the space necessary for the many series of pits and drums.

The scope of the present invention is to bring the suitably prepared bovine hides into contact with concentrated solutions of vegetable tannin, under such conditions as to avoid surface tanning, thus permitting the subsequent rapid diffusion of the tanning agent into the internal layers of the hides until tanning is complete. Furthermore, in the process here claimed, the preparation of hides for tanning is quickly performed, and some preliminary operations which were previously necessary are eliminated. in the following I describe in chronological order, the steps necessary for vegetable tanning of sole leather, according to conventional methods, compared With those of the process claimed.

Tanning-Acid Soaking:

This step has the scope of bringing the hides to the conditions existing at the moment of slaughtering the animal and is carried out in pits 0r drums, diving the hides in water. It requires one or two days according as to whether the hides are fresh salted or dry salted Liming:

This step is carried out for dc-hairing the hides and consists in treating the hides with calcium hydroxide and sodium sultitle, in pits or better in drums. The

process requires two days using 8l8% lime and 1.53% sodium sulfide according to the quality of the hides or of the required final product Delirniug:

Pro-Tanning or Fixing of the Grain:

It is nowadays common in conventional systems to precede true and proper tanning with a pro-tanning process, mainly using special nonvcgetable tanning substances, commonly known as synthetic tannins, and

Working in drums with l.5-3% of these products, followed by Washing under running water. This operation requires 1 day. Fixing of the grain is also performed in the system claimed, using a polyglucosylol-bisulfite such aS for instance dialdehydc starch Incnobisulfitc for at most an equal period of time Dyeing:

In conventional processes the hides are brought into contact for 2 or 3 days With dilute and aged solutions of vegetable tanning agents, in pits with circulating or non-circulating liquid. This step is not performed in the process claimed Tanning in Depth:

Tanning-Fixing:

In this stage the hides are placed in drums with highly concentrated vegetable tanning solutions, that is, of 12l4 B., for a period of 2 days, at C, in order to obtain the most possible complete fixing of tannin on the dcrmic substances. In many cases the drum is replaced by a pit at 40-45" 0., containing more concentrated tanning solutions, i.e. at 19 Be, the hides being treated for 6 days. By the claimed process the whole tanning is performed in drums at a l2-15 Be. concentration of the vegetable tanning agent, for a duration of ays- RcTanning, Dressing and Finishing:

Patented Dec. 17, 1963 DllIatiOn, days q v Claimed M01131 process processes 1 not performed 2-3 not performed 15-30 not performed min. 34, min. 16,

max. 55 max. 17

By the most important embodiment of the process, fixing of the grain is carried out with polyoxysaccharidebisulfites, compounds obtained by combining sodium or ammonium bisulfite with one or both aldehyde groups of each glycoside unit of polyoxysaccharides.

The polyoxysaccharide which gives the best results is dialdehyde starch, which is preferably used in the form of the monobisulfite derivative, although the di-bisulfite compound still gives entirely satisfactory results.

These products may be prepared separately, before use in tanning, or else they may be formed in situ, in the tanning bath. The molar ratio between the amounts of polyoxysaccharide and bisulfite vary according as to whether it is wished to obtain a prevalent amount of monoor dibisulfite, and therefore range from 1:1 to 1:2. All bisulfite compounds of this type exert their tanning action in alkaline media and the alkalinity of the hides themselves, due to the presence of lime and sodium sulfide, is used for this purpose.

Thus, it is apparent that the process claimed produces conditions suitable for the fixing of polyoxysaccharidebisulfites, with the advantage of eliminating most of the lime retained in the hides, in the form of soluble bisulfites. Furthermore, the presence of some residual lime in the hides at the moment of vegetable tanning, favors penetration of the tanning agent as the astringency of the same is decreased and the reaction between proteins and tannin is by far less vigorous in the first steps of tanning. The amount of product to be used is related to the degree of penetration to be reached and ranges from a minimum of 2.5% to a maximum of 20% for total penetration of the hide.

The following examples, which must not be considered as limiting the invention, indicate the typical operating conditions:

Example 1 One hundred kilograms of soaked and Washed butt are placed in a drum with 350 litres of water and 10 kg. of calcium hydroxide and rotated for 10 minutes. A solution of 2.2 kg. of 30% hydrochloric acid in 20 litres of water are then added, the drum is rotated a further 10 minutes and, finally, 3 kg. of sodium sulfide dissolved in 8 litres of hot water are added. The drum is rotated for three hours and then stopped, afterwards rotating minutes every hour, for a total of 48 hours. The hides are then fleshed and bated.

Three hundred kilograms of fleshed and hated butt are placed in a drum with 400 litres of water, five kilograms of dialdehyde starch monobisulfite in powder form are r added and the drum is rotated for 12 hours at 4 rpm. The initial pH of the solution is 7, and the final 9.6. The solution is then run oil and the hides thoroughly washed for about an hour. Still in the same drum, 230 litres water and kg. of sweetened chestnut extract in powder form are added to the hides, rotating them for 30 minutes at 4-5 rpm. After this stage the bath has d:2.5 B. and pH=4.5. Sixty kilograms of sweetened chestnut extract in powdered form are added to the same bath and the drum rotated for a further 47.5 hours. At the start of the 2nd addition the bath has d=12.5 B. and pH:4.6, while at the end of rotation the following values are found: d=8.2 B. and pH=4.6. The residual bath, after suitable strengthening, may be re-used for subsequent operations or for other tanning purposes.

Example 2 One hundred kilograms of soaked and washed butt are treated with calcium hydroxide, sodium sulfide and hydrochloric acid as in Example 1. One hundred kilograms of fleshed and heated butt are placed in a drum with 5 kg. dialdehyde starch and 3.25 kg. powdered sodium bisulfite, rotating for 12 hours in the same conditions as in Example 1.

The two above-mentioned substances are in equimolecular proportions, that is, 1 mole of anhydrous dialdehyde starch per mole of anhydrous sodium bisulfite. The hides are then tanned with sweetened chestnut extract in powder form, as described in Example 1.

Example 3 One hundred kilograms of soaked and washed butt are treated with calcium hydroxide, sodium sulfide and hydrochloric acid as in Example 1 and then pre-tanned with 10% polyoxysaccharide-monobisulfite derived from oxycellulose, under the same conditions as described in Example 1.

Example4 One hundred kilograms of soaked and washed butt are treated with calcium hydroxide, sodium sulfide and hydrochloric acid as in Example 1, pre-tanned with 2.5 kg. dialdehyde starch and 3.2 kg. powdered sodium bisulfite, under the same conditions as described in Example 2 and then tanned as described in Example 1. The two products are in the molar ratio or 1:2 that is, 1 mole of anhydrous dialdehyde starch per 2 moles of anhydrous sodium bisulfite.

Example 5 One hundred kilograms of butt are treated with calcium hydroxide and sodium sulfide and hydrochloric acid as indicated in Example 1 and pre-tanned as in Examples 14, then initially tanned with 10% sweetened chestnut extract in powder form, followed by a mixture of 40% sweetened chestnut extract and 20% normal chestnut extract, related to the hide weight, as described in Example 1.

Example 6 One hundred kilograms of butt are treated with calcium hydroxide, sodium, sulfide and hydrochloric acid as in Examples 1 to 4 and then initially tanned with 10% solid extract of soluble quebracho, followed by 60% solid extract of soluble qucbracho as described in Example 1.

Example 7 One hundred kilograms of butt are treated with calcium hydroxide, sodium sulfide and hydrochloric acid as in Examples 1, 2, 3 and 4, and are then initially tanned with 10% dry mimosa extract followed by 60% dry mimosa extract as described in Example 1.

Example 8 One hundred kilograms of non-delimed bovine hides are treated with 300% by weight of water, 10% of anhydrous sodium sulfate and 2% of sodium carbonate. Into the same solution, previously adjusted to pH 7.0, dialdehyde starch monobisulfite in a ratio of 4.1% by weight is added and the pH is maintained at a constant value of 88.5 by the addition of sodium carbonate. After washin g the hides, which are thus pre-tanned, are tanned with vegetable agents as described in the preceding examples.

Example 9 The procedure of Example 8 is repeated, except that an 3.2% ratio of dialdehyde starch monobisulfite is used.

Example 10 One hundred kilograms of delimed bovine hides are treated with 300% by weight of water and 10% of sodium sulfate, then 4.1% of dialdehyde starch are added, followed by sodium carbonate sulficient to obtain pH 8-8.5.

Example 11 The procedure of Example 10 is repeated with an 8.2% ratio of dialdehyde starch monobisulfite.

I claim:

1. Process for rapid tanning of sole leather consisting in treating the hides for 12-24 hours at a pH over 5, with 120% by weight of a polyoxysaccharide-bisulfite in 5 6 Water, then tanning the hides thus treated with a concen- 4. Process as in claim 1, in which the polycxysactiated solution of vegetable tanning agent. charide bisulfite is dialdehydestarch di-bisulfite.

2. Process as in claim 1, in which the nuclear ratio between polyoxysaccharide and bisulfite in the poiyoxysac- References Cited in the filfi Of this Patent charide bisulfite lies between 1:1 and 1:2. 5 UNITED STATES PATENTS 3. Process as in claim 1, in which the polyoxysac- 2,886,401 WEHS et a1 y 1959 charide bisulfite is dialdehydestarch monobisuifite. 

1. PROCESS FOR RADID TANNING OF SOLE LEATHER CONSISITNG IN TREATING THE HIDES FOR 12-24 HOURS AT A PH OVER 5, WITH 1-20% BY WEIGHT OF A POLYOXYSACCHARIDE-BISULFITE IN WATER, THEN TANNING THE HIDES THUS TREATED WITH A CONCENTRATED SOLUTION OF VEGETABLE TANNING AGENT. 